1. Field of the Invention
The field of the invention relates to spring-return actuators.
2. Description of the Prior Art
U.S. Pat. No. 3,122,351 to Brown discloses a spring-driven actuating mechanism for low torque valves which utilizes a clock spring 26 within drum housing 21 and cylindrical hub sleeve 27 of mounting plate 20. When valve plug 13 is "open" latch finger 28 is urged into latching position via spring 30.
Pressure in the control line maintains latch finger 28 in latching position whereas a drop in pressure releases the latch whereby the clock spring will close the valving member.
U.S. Pat. No. 3,306,317 to Brown discloses a high and low pressure-responsive actuator mechanism for plug-type valves wherein the means by which clock spring torque is applied to the stem of a plug valve 13 is substantially the same as in U.S. Pat. No. 3,122,351, supra. The primary difference in said patents being that in U.S. Pat. No. 3,306,317 the latch-release means are responsive to either high or low pressures.
U.S. Pat. No. 1,292,267 to Dawson, et al, discloses an energizing or tensioning device for spiral springs wherein one end of a spring is connected to a fixed part and the other end of the spring is attached to an oscillating shaft.
U.S. Pat. No. 3,161,014 to Abild discloses a spring-driven actuator mechanism where a spring is interposed between a driving means and a driven member, and wherein the driven member and the driving means are separated in response to a signal thereby enabling the spring to actuate the driven member.
U.S. Pat. No. 3,279,744 to Fieldsen, et al, discloses a valve actuator wherein the valve-closing action of spring 57 is opposed by the electrically operated brake of an electric motor which opens the valving member against the counter-force of spring 57.
U.S. Pat. No. 3,592,991 to Turner, et al, discloses a torque converter which utilizes the energy storing capability of a torsion spring connecting an input and an output shaft to provide a uniform driving force on the output shaft throughout the final arc of movement of the output shaft irrespective of the speed at which the input shaft is rotated so as to provide a uniform high terminal velocity to a switch plate upon closure without sufficiently high impact to damage the spring-actuated switch.
U.S. Pat. No. 3,808,895 to Fitzwater discloses an electrically operated fail-safe valve actuator which utilizes a spring which is wound to store energy during the operation of an electrical drive motor and which includes an electric clutch operable to disengage the drive motor from the actuator output shaft in response to a loss of power whereby the spring will drive the valve in the opposite direction.
U.S. Pat. No. 3,889,924 to Karpenki discloses a valve stem operator in which a threaded valve stem is moved by a jack-nut to open and close the valve. The jack-nut is connected to a drive arbor which is selectively rotated by either the motor or a clock spring. A clutch situated between the worm gear and the drive arbor is fixed by an air cylinder to engage the gear and arbor to allow the motor to open or close the valve. Upon failure of the motor control either the air cylinder or a biasing stripper spring shafts the clutch out of engagement whereupon the clock spring rotates the drive arbor and jack-nut to move the valve stem automatically in a prescribed direction.
Applicant is unaware of spring-return actuators of the type which include a safety clutch which is constructed and arranged in such a manner as to insure that the potential energy within the spring of the spring-return will be completely dissipated before access to the interior of the spring-housing may be accomplished.